Aerobic Biodegradation of Polyhydroxybutyrate in Compost

Abstract

Aerobic biodegradation of polyhydroxybutyrate (PHB) was investigated. Mass loss experiments were performed to determine degradation kinetics. Tributyl citrate was blended with some test samples to determine the impact of a natural plasticizer on biodegradation. Effects of biodegradation in the physical, chemical, thermal, and mechanical properties of the materials tested were determined. Plates of different thicknesses (0.24, 1.2, 3.5, and 5.0 mm) were degraded to determine the effect of initial mass:initial surface area ratio on degradation rates. The mass:initial surface area is proportional to the plate thickness. PHB biodegradation rates obtained are dependent on the mass:surface area ratio. Temperature affects the relation of degradation rate to initial mass:initial surface area. PHB in plates up to a thickness of 3.5 mm can degrade completely in compost. Plates with an initial mass:initial surface area ratio of <67 will degrade in <4 months. Maximum degradation rates were obtained in plates 3.5 mm thick (1.57 mg cm−2 d−1) and the minimum in plates 0.24 mm thick (0.16 mg cm−2 d−1). Less than 14% degradation was observed in plates 1.2 mm thick with the additive tributyl citrate, compared to 100% for the plates of the same thickness without additive. No change in relative composition of molecular bonds, molecular weight, or thermal properties were observed. Impact strength of the specimens show little change until a significant loss of structure is observed.